In a conventional semiconductor device manufacturing process, after a semiconductor chip is mounted on a substrate, a molding process to mold the substrate and the semiconductor chip with resin is carried out for the protection of the semiconductor chip. After the molding process, in order to remove residual stress of the resin, a curing process is performed in order to reheat the resin and return it to room temperature. Japanese Patent Application Publication No. JP-A-4-313245 discloses a method for manufacturing a semiconductor device that includes curing the semiconductor device, after it is molded with resin, while applying a pressure to hold it flat.
In a single-side molded package that is typical for a ball grid array (BGA), only a surface of a substrate where a semiconductor chip is mounted thereon is molded with resin. Accordingly, the semiconductor device has a double layered structure that includes the substrate and the resin. It should be appreciated that because of the difference in coefficient of thermal expansion between the substrate and the resin, during the heating processes associated with the aforementioned molding and curing operations, warpage in the semiconductor device occurs. When warpage is large, errors in delivery and by adsorption to jigs in a later process may result. As a result, yield rate is decreased and the cost of the semiconductor device is increased.
In a conventional method, in order to reduce warpage, slits are provided on a substrate, to divide the resin into smaller divisions. However, in this method, the use of the substrate and the resin is less efficient which results in a higher cost. Further, when a substrate is made larger in an attempt to improve the efficiency, warpage increases.